From Fractal Urban Pattern Analysis to Fractal Urban Planning Concepts - Computational Approaches for Urban Environments - page 40

Tabl e 2. 5 Number of central
places by their facility level

Level Number

1 1

2 4

3 20

4 100

This type of hierarchy is consistent with the logic of fractal structures. Here, too,
additional morphological rules are introduced which avoid green corridors being cut
up or isolated green islands being generated.
We introduced, too, a population model. It affects to each of the square-like
zones a population which takes into account its size as well as its hierarchical
level. This model can also attribute a certain population to the various rural areas
cut off in the course of iteration. Starting from real population data, the simulation
tool identifies the population in the various zones defined by the simulation and
computes the mean population for each hierarchal level. The simulator shows for
each city the surplus or deficit with respect to this mean number. Moreover, the
model can define distribution laws according to the underlying hierarchical logic
and hence propose population development scenarios. Details are presented in a
working paper (Frankhauser 2012 ).
Figure 2.15 shows the different steps for a simulation of the metropolitan area of
Lyon. Here, the colors refer to the population surplus or the deficit with respect to
the mean values for the different hierarchical levels.

2.6.3 The Accessibility Rules

For both planning concepts presented here, the accessibility to different types of
amenities frequented by residents is one of the fundamental aspects. Indeed, as
pointed out, the accessibility to different types of amenities offered to the inhabitants
is fundamental in order to propose planning scenarios that can reduce the total length
of trips. Moreover, it is possible to clearly identify accessible sites which could be
developed in the future. Both “urban” (goods and services) and “rural” amenities
(green leisure areas) are considered. By the underlying central place logic, which
appears explicitly in the Fractalopolis coding system, different levels of amenities
are distinguished depending on how often residents use them. We present here the
methodology developed for measuring accessibility to retail and service centers
(Frankhauser et al. 2011 ). For a medium-sized agglomeration, we distinguish three
service levels:

￿ Level 1 (monthly use of less occasionally attended places such as medium

and large specialized stores, town halls, banks/insurance companies, restaurants,
cinemas, theaters, etc.). Since it is unlikely that new centers of this level will be